Maintaining a proper pelvic posture and providing stability through the pelvis are critical to overall sitting posture. Freedom of movement can be enhanced by achieving a stable base of support. The optimum position for the pelvis is a slight anterior tilt. An effective pelvic support will prevent the pelvis from tilting posteriorly. A posterior pelvic tilt promotes rounding of the upper spine, which can lead to deformity. For a pelvis which posteriorly tilts, the top of the pelvis must be blocked from moving back and the bottom of the pelvis must be stabilized from moving forward. With adequate proximal support, less support is required distally. Therefore, with increased stability of the pelvis, the user is less dependent upon additional supports in order to maintain a functional, upright sitting posture. Individuals using wheelchairs need assistance to maintain pelvic stability.
The neutral posture of the pelvis is a dynamic state which should be allowed to move. Therefore, a rigidly stabilizing pelvic position is not desirable. Currently available pelvic supports either do not control undesired pelvic movement, or lock the pelvis in a static, non-functional position. The subtle movements of the pelvis are critical to maintaining an active posture and should not be rigidly stabilized.
Currently available pelvic stabilization devices do not move with the user and do not provide a dynamic force to help correct the user's posture after allowing movement. Pelvic support devices which do not maintain contact with the pelvis when the user moves are less effective. Currently available devices do not support the pelvis from the front, back, and sides. A combination of devices, often from various sources, must be used to provide support in these areas. This increases the cost of the seating system, adds bulk and weight, and increases time required to install, fit, and adjust the system for growth. Potential hazards presented by improperly used pelvic include strangulation from sliding out of an ill-fitting system, and tissue damage due to high pressures from rigid anterior pelvic supports.
The following is a summary of currently available pelvic supports, with their deficiencies.
Wheelchair Setup: Orientation-in-Space (OIS): Tilting the wheelchair back uses gravity to hold the pelvis against the backrest. In this position it is difficult for the user to move the pelvis, trunk, and head. The user is left facing upward in a nonfunctional position. Tilting the seat forward activates extension muscles of the trunk and can be used only for short periods (e.g., 15minutes).
Seating Components
Anti-thrust seat (ATS): This type of seat provides a rear section which is lower than the front section. This is designed to hold the pelvis to the rear of the seat. However, the seat height transition can be a source of high pressure, and the pelvis, if not held securely, can move over the transition.
Contoured seat: This type of seat is shaped to conform to the user. It is designed to distribute pressure at the seat surface. The cushion's sloping shape often causes the hips to slide into improper postures. This seat is custom made and cannot be adjusted for growth or change.
Bi-angular back (BAB): This type of backrest provides rear support for the sacrum and upper pelvis. If the front of the pelvis is not supported properly, the BAB can push the user forward in the seat.
Lateral hip pads: These are used at the sides of the hips and are only effective in preventing the pelvis from moving laterally. They do not address lateral tilting of the pelvis.
Anterior pelvic supports
Lap belt: A single attachment lap belt used at a 45 to 90 degree angle to the seat surface is flexible and useful for controlling mild pelvic movement.
Four-point lap belt (translated pivot point): This device can provide more stability than a single attachment lap belt. However, it allows some movement of the pelvis and must be used with a sacral support to provide effective control of pelvic tilt.
Pelvic stabilizer (wide abduction pommel): This device is designed to apply an anterior force to the pelvis at the pubic bone. The pelvic stabilizer can be effective in maintaining the rearward position of the pelvis in the seat. However, if not monitored closely, this device can damage soft tissues.
Sub-ASIS bar: A straight or curved sub-ASIS bar is a rigid, padded bar designed to hold the pelvis just under the ASIS. It tends to be difficult to properly fit and can produce high pressures and tissues damage at the front of the pelvis.
Anterior knee blocks: This device is designed to apply a rearward force at the knee that is transmitted through the femur to the hip joints. This device allows forward tilting of the pelvis, and it relies upon the countering force of a sacral support. Anterior knee blocks and straps can cause further joint problems for users with compromised hip integrity. Some controversy exists about the practice of applying a constant force to the knee and hip joints, particularly in cases where high tone is present.
The following patents all pertain to wheelchairs and support devices therefor.
U.S. Pat. No. 5,678,798 discloses a swing support bracket assembly for mounting support pads to wheelchairs. The assembly includes a housing, an axle mounted for rotation in the housing, and a toggle pivotally mounted in the housing and having a tapered protrusion adapted to engage a cooperating tapered recess in the axle. The support pad may be mounted either directly or by a number of adjustable clamps and support rods to the housing. In another embodiment it is mounted by such rods and clamps to the axle.
U.S. Pat. No. 5,564,788 discloses a support system for maintaining a person in a substantially upright sitting position in a wheelchair, comprising a unitary frame and a unitary cushion. The unitary frame has front and back portions, and a generally rectangularly shaped central portion having upper and lower sections. A pair of upper lateral wing frame portions extend from the upper section of the central portion, and a pair of lower lateral wing frame portions extend from the lower section of the central portion. The unitary cushion is shaped to fit over the frame and comprises a generally rectangularly shaped central cushioned portion having upper and lower sections, a pair of upper lateral cushioned wing portions extending from the upper section of the cushioned central portion and a pair of lower lateral cushioned wing portions extending from the lower section of the cushioned central portion. The pairs of upper lateral wing frame portions and lateral cushioned wing portions, provide bracing to the left and right sides of the person's upper torso in a substantially upright position. The pairs of lower lateral frame wing portions and the upper lateral cushioned wing portions, prevent rotation of the person's pelvis. Each of the upper lateral wing frame and cushioned portions, the central frame and the cushioned sections, and each of the lower lateral frame and cushioned wing portions, are generally C-shaped when viewed from the side.
U.S. Pat. No. 5,447,356 discloses a chair for disabled persons with a supporting frame, a seat adjustably connected to the supporting frame by a hinge, and a back adjustably connected by a hinge to the rear of the seat. The seat has a front section which lies beneath and supports the upper legs of an occupant, and a rear section which lies beneath and supports the pelvis of an occupant. The front and rear sections can be fixed and adjusted independently of each other due to a hinge which is parallel to the hinge at the rear of the seat.
U.S. Pat. No. 4,813,746 discloses an angular bar mounted on each opposing lower portion of a wheelchair frame for securement of the pelvis of a person seated in the wheelchair. Each bar has a side portion that extends across the lateral region of the hip and a front portion that extends in front of the hips above the thighs. Universal adjustments with a quick release mechanism are provided for independent adjustment of each arm.
U.S. Pat. No. 4,073,537 discloses a device for positioning a patient in a chair having a back and arms. The device includes a pad for placement against the patient and a clamp which underlies an arm of the chair and is shiftable along the length of the arm independently of the back. The pad is connected to the clamp by a series of connecting members which permit universal swinging of the pad about a plurality of angularly disposed and laterally spaced axes. The pad also is mounted for shifting laterally of the attaching clamp and the arm to which it is attached and for shifting vertically and horizontally forwardly and rearwardly relative to the chair. A locking mechanism is provided for securing the pad in any of the infinitely selectable positions for the pad to maintain patient positioning with in the chair. A similar pad attached to the opposing arm on the chair also may be used to aid in patient positioning.
U.S. Pat. No. 3,640,571 discloses a trunk support for use with wheelchairs and the like having contoured trunk support plates disposed laterally of and in supporting contact with the patient's trunk. The plates are secured to the backrest of the chair, are universally moveable for adjustment to the patient's size and shape, and are locked in the supporting position. The plates can be opened to permit the patient to enter or alight from the chair. Stop means are provided so that each time the plates are moved into their trunk supporting position they return to an identical, predetermined position to thereby eliminate the need for adjustments of the plate while used with the same patient.
U.S. Pat. No. 3,704,910 discloses a cushioned torso engaging member adapted to be mounted to one or the other of the handles of a conventional wheelchair or the like either alone or in pairs, by means of an assembly of a handle clamp and linked arms which provide both for angular, elevational and dimensional adjustment of the position of the torso engaging member relative to the wheelchair handle.